Based on wave theory, wave information is not limited to amplitude, frequency, phase of wave, but also includes various spatial motion properties such as vibration nature and direction of a wave field, divergence and curl vectors of a force field, etc. These spatial motion properties include abundant information that is indispensable to wave research, which play important roles in aspects such as wave field separation, signal-to-noise ratio, fidelity, imaging precision, medium attribute analysis, or the like. However, an existing seismic acquisition and detection technology can only detect information such as amplitude, frequency, phase or the like, and could not detect the spatial properties of wave motions.
For this reason, the related art proposes an omnidirectional vector seismic wave detector, which builds a space vector structure according to a field theory formula in a basic unit of a high performance mature commodity electromagnetic and capacitive seismic detector, to realize detection of full information of the seismic wave field.
But the seismic wave detector in the prior art has a very big defect, which affects further improvement of performance of an omnidirectional vector geophone that is built in a unit device of the seismic wave detector, this is a question of relative motion: there must be a relatively immovable reference system for measurement of any motion and vibration. Generally the ground which is immovable is taken as reference. How to build an immovable reference system for measurement of ground wave and vibration is an important and difficult question.
A traditional wave detector supports a mass block by spring suspension, and this problem is solved by a method of causing relative motion between the mass block and the ground by delay of a spring. But inverse relation between a K coefficient of the spring and the delay is the defect. The softer the spring is, the longer the delay is, the larger the relative motion is, the higher the sensitivity is, the worse the fidelity is; the harder the spring is, the shorter the delay is, the better the fidelity is, the lower the sensitivity is. If the mass block moves synchronously with the ground, there is no delay, and although the fidelity is good, there is no relative motion, the sensitivity is zero, then the wave detector fails. Thus it can be seen that the sensitivity and the fidelity become a pair of contradictions. So all the time, design and manufacture of the spring in core technology of the wave detector is extremely important.
Explanation is made by the following formulas:
a spring force balance formula: (g+a)m=−kx,
a spring vibration formula:
      x    =          A      ⁢                          ⁢      cos      ⁢                          ⁢              (                                                            k                m                                      ⁢            τ                    +          φ                )              ,
a spring wave detector output formula:
      U    =          T      ×                                                  (              a              )                        ⁢            m                    k                ·        sin            ⁢                          ⁢                        (                                                                      k                  m                                            ⁢              τ                        +            φ                    )                ·                  e                      -            rτ                                ,
wherein, x denotes displacement of the mass block/spring vibrator; A denotes wave field amplitude; U denotes output; T denotes magnetic field strength, and if is replaced with electric field strength, it is the function of x; a denotes an acceleration to be measured; m denotes mass of a mover system; k denotes a spring coefficient; τ denotes system response time; φ denotes phase; and r denotes a damping coefficient.
It can be seen from the above several formulas that, k is at a denominator position when affecting the sensitivity, and the smaller the better; and k is at a numerator position when affecting the fidelity, and the larger the better.
An MEMS wave detector is a capacitive-type representative, FIG. 1 is a schematic diagram of operating principle of an MEMS capacitive wave detector according to the related art, as shown in FIG. 1, the MEMS wave detector is provided with a spring for connecting a mass body and a frame. The MEMS wave detector converts part of support force into sensitivity by a capacity based distance measuring in cooperation with an electrostatic force negative feedback technology, which partially solves the problem, and thus performance indicators have been greatly improved.
If the support force can be totally converted into sensitivity, fidelity and sensitivity can be combined ideally, then the performance indicators may be improved more greatly. But due to space structure problem, force balance of the existing MEMS wave detector is not three dimensional, it can realize levitation in a three-dimensional space not merely depending on electrostatic force, and also needs a spring structure for supporting, thus contradiction between the sensitivity and the fidelity still exists such that improvement of performance thereof is limited.
It can be seen based on the above analysis on operating principle of the capacitive wave detector that, a spring is a key factor for restricting the sensitivity and the fidelity. An electromagnetic type wave detector is even more supported totally by a spring, spring resonance plays a dominant role and has worse performance.
It can be seen based on the above analysis on operating principle of the MEMS wave detector that, the spring plays a non-negligible role and still restricts improvement of the performance.
FIG. 2 is a schematic diagram of directional response of an ideal single wave detector in a pressure wave field, and FIG. 3 is a schematic diagram of directional response of the ideal single wave detector in a shear wave field, for describing operating directivity of the wave detector. As shown in FIGS. 2 and 3, the output of a wave detector is realized based on the formula: out=A⋅n=a×b cos θ. Wherein, A denotes wave field function and vector; n denotes a unit vector of the wave detector in the operating directivity; a denotes instantaneous amplitude of a wave field A in a vibration direction; b denotes sensitivity of the wave detector; θ denotes an angle between the operating direction of the wave detector and the vibration direction of the wave field at position of the wave detector; p denotes a pressure wave subscript; S denotes a shear wave subscript.
Specifically as shown in FIG. 2, the output of a wave detector in the pressure wave field is realized based on the following formula:
out=Ap⋅n=ap×b cos θp; wherein, Ap denotes an isochronous surface of the pressure wave field; ap denotes an instantaneous displacement of the wave field Ap in a normal direction at the position of the wave detector; b denotes sensitivity of the wave detector; θp denotes an angle between the operating direction of the wave detector and the vibration direction of the wave field.
As shown in FIG. 3, the output of a wave detector in the shear wave field is realized based on the following formula:
out=As⋅n=as×b cos θs; wherein, As denotes an isochronous surface of the shear wave field; as denotes an instantaneous displacement of the wave field As in a vibration vector direction at the position of the wave detector; b denotes sensitivity of the wave detector; θs denotes an angle between the operating direction of the wave detector and the vibration direction of the wave field.
FIGS. 2 and 3 and the above formulas do not include other performance of an electromagnetic capacitance wave detector, only include directional description. The above formulas are only used for describing a single wave detector, which satisfies directional requirement of multi-dimensional space structure.
Assuming that all wave detectors have the same sensitivity, b can be used as a constant, or can be made equal to 1, which has no influence on mathematical physical significance. A wave field amplitude extreme value can also be regarded as being stable in a local area that is much larger than volume of the wave detector, and can be temporarily regarded as a constant in consideration of response of the wave detector.
Although the electromagnetic capacitance wave detector has an operating direction, on the basis that a single wave detector outputs a single known variable, two unknown numbers including a primitive function and an angle cannot be solved from only one equation.
In conclusion, the existing wave detector has the following defects:
1. A common wave detector has no functions of detecting curl, divergence and vector, and it detects a projection of the vector, as shown in FIG. 2; a hydrophone can detect divergence, but has no functions of detecting a curl vector and a linear vector; a three-component wave detector is an orthogonal combination of three directivities as shown in FIG. 2, has a function of detecting a linear vector but has no function of detecting divergence or curl.
2. In all spring support structures, sensitivity and fidelity are mutual restrictive, so that performance improvement capability is limited.
3. Curl and linear vector separated structure in research and development has a large overall volume.
4. There is no curl and linear vector same-mechanism structure.
For the above defects in the related art, there has not yet come up with an effective solution.